Backbone of the Americas—Patagonia to Alaska, (3–7 April 2006)
Paper No. 5-6
Presentation Time: 10:35 AM-7:45 PM


BRIDGES, David L. and GAO, Stephen S., Department of Geology, Kansas State University, 108 Thompson Hall, Manhattan, KS 66506,

The frequency-magnitude distribution was spatially mapped beneath Makushin Volcano, Unalaska Island, Alaska. The final earthquake catalog used in this study consists of 491 events that occurred between July 2001 and April 2005. Two high b-value anomalous zones were found, one ~4 km east of the Makushin's main vent area at a depth of 3 km to 7 km (b ~ 1.8) and a second one located 7 km southeast of the vent (b ~ 1.6). The significance of this second volume could not be tested statistically due to its small dimensions and the low number of seismic events in its proximity. The first anomaly is robust statistically based on Utsu's (1992) p-test and is not method or parameter dependent. This anomaly suggests the presence of crustal heterogeneity and/or high pore pressure, such as that typically found near magma chambers, at ~6-7 km depth. Our results agree with the findings of an InSAR interferometric study which suggest the existence of a magma chamber at ~7 km depth, 5 km east of Makushin's vent.

Backbone of the Americas—Patagonia to Alaska, (3–7 April 2006)
General Information for this Meeting
Session No. 5
T5. Processes, Comparisons and Other Cordilleran Issues I: Seismicity, General Tectonic Processes, and Specific Examples
Congress & Exhibition Center: Foyer and Auditorio Bustelo
10:35 AM-7:45 PM, Monday, 3 April 2006

Geological Society of America Abstracts with Programs, Speciality Meeting No. 2, p. 55

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